An example of relationship between flow of transmit power control of CDMA mobile communication system by the prior art and radio slot configuration is schematically shown in FIG. 1.
As shown in FIG. 1, 1) received signal power measurement is performed for each transmit power control section (hereinafter referred to as “slot”), 2) the measurement result is subjected to a division calculation using a measurement result of noise interference power to obtain a received SNIR (signal power to interference power ratio), the received SNIR is compared with a reference SNIR, 4) a transmit power control bit is transmitted designating a transmit power control indicator of the received side channel, so that when the comparison result exceeds the reference SNIR, a base station transmit power is decreased, or when the comparison result is below the reference SNIR, the base station transmit power is increased.
As shown in FIG. 1, in the traffic channel, there exists not only a fixed transmit part (shaded in FIG. 1) in which the number of transmit bits is unchanged, but also a variable transmit part in which the transmit bit number is successively changed according to a change in information speed of transmitted data, when there is no data, transmit is stopped. In this case, the fixed transmit part is applied to received signal power measurement.
As shown above, received signal power measurement in a CDMA reception apparatus is performed using a fixed transmit part, however, there is a problem that when signal power of the fixed transmit part is small, measurement accuracy of received signal power is deteriorated, and transmit power control is not performed with good accuracy.
As described above, accuracy degradation of transmit power control has resulted in an increase in transmit power and deterioration of channel capacity.